This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A138718 #2 Mar 30 2012 17:33:54 %S A138718 1,2,3,4,5,6,7,8,8,8,1,2,3,4,5,6,7,8 %N A138718 Group number of the elements of the n-th column of the periodic table of the elements with 18 columns. %e A138718 Columns of The Periodic Table of the Elements: %e A138718 1...2...3...4...5...6...7...8...9...10..11..12..13..14..15..16..17..18. %e A138718 A notation convention of the groups is %e A138718 1A, 2A, 3B, 4B, 5B, 6B, 7B, 8B, 8B, 8B, 1B, 2B, 3A, 4A, 5A, 6A, 7A, 8A. %e A138718 Then the sequence of this entry is formed from the numeric characters: 1, 2, 3, 4, 5, 6, 7, 8, 8, 8, 1, 2, ... %e A138718 Note that the elements, of the 4th period, whose crystals are ferromagnetics (26=Fe=Iron, 27=Co=Cobalt and 28=Ni=Nickel) are in the group 8B. %Y A138718 Cf. A138723, A138724. %K A138718 easy,fini,full,nonn %O A138718 1,2 %A A138718 _Omar E. Pol_, Mar 27 2008